Attribute aggregation is collating attributes about a user account from multiple sources. In the case of virtual organizations and their use of specific web resources with federated login, this boils down to: how do I add an eduPersonEntitlement maintained by VO-whatnot to the information about the user from his university.

The possibilities and the doors opened with attribute aggregation are enticing and slightly frightening. My international research project site getting an attribute from the project manager and federated login from my employer will work fine. That is not scary. The employee web site may be able to download info about my color preferences from nerdy-color-repository. That is not so scary. When my son starts school next year, I may log in to the learning management system, getting the login from the national eID, the association with my child from an attribute authority and information about his attributes from Feide. That is cool and not scary at all. The pizza place getting info about my phone number, cross referencing with payment history, getting info on pavement status in my neighbourhood and refusing to dispatch pizza to the people helping me move my piano. That is scary. And partly why the user interface for aggregation, informed choices, privacy, security testing and a lot of other issues needs more work.